The paper aims to show the uneven process of integration of Polish manufacturing into the Single Market due to differentiational changes in competitiveness across industries (third digit level of NACE Rev. 1.1 classification) in 1996-2001. It starts with a discussion on the nature and measurement of competitiveness. Since this notion is derived from that of competition as rivalry, the effects and factors of competition are the focus. Section 2 describes the overall picture of changes in competitiveness of Polish manufacturing measured by changes in market shares and relative labour productivity. Changes in relative unit export values as a measure of changes in quality of products produced in Poland are considered. Section 3 analyses the usefulness of various measures of changes in the competitiveness of Polish manufacturing in depicting the uneven process of integration of industries into the Single Market. In the last section the winners and losers in the process of integration of Polish manufacturing into the Single Market and the factors determining uneven integration are analysed.